The Genetics of Split Wing – Part 1

Since we have found split wing in our newly purchased chicks (not knowing previously anything about split wing), and we are breeding our chickens, I have been doing some research on split wing and how it is passed along genetically so we can make informed decisions about our breeding stock.

Split wing is reported to be an autosomal recessive gene.  Here is how that works:

Each parent carries two genes for the trait (this particular trait being called split wing).  They each give one of their genes to their offspring, thus each offspring has one gene from the father and one from the mother.  The easiest way to picture this is to draw a chart showing the mating of the two parents and what genes statistically four of their offspring would carry.  We give the trait genes letters to represent whether the gene is dominant or recessive.  A dominant gene overrides a recessive gene as far as whether or not the trait is actually actively present in the animal.  We write dominant traits with a capital letter and recessive traits with a lowercase letter.

In the below example chart you can see that the father’s genes are listed across the top, in this example he carries RR.  The mother’s genes are listed down the side, in this example she carries Rr.  And the four offspring’s genetic possibilities are listed in the boxes.  One offspring could get a R from the father and a R from the mother, thus making that one’s genetics for that trait RR.  Another offspring could get a R from the father and a r from the mother, giving that offspring the genetics Rr for that trait.

So if the below mating took place, statistically 50% of the offspring would carry the genetics of RR, and 50% would carry the genetics of Rr for this specific trait.

103_0522So let’s look at the genetics for an autosomal recessive, like split wing.

R is a normal wing, and r is a split wing.  But we are dealing with two genes for the trait, so here is how it plays out:

  • Any bird that has RR (the dominant genes) does not have split wing at all and cannot even pass the genes for split wing on to their offspring.
  • A bird that has rr actively has split wing (their wing shows the split) and can pass it on to their offspring.
  • A bird that has Rr does not actively have split wing (their wings look fine) BUT this bird carries the gene of r and can thus pass it on to their offspring even though their own wings are normal.  The Rr birds are called “carriers” because they carry the gene in their DNA, but you can’t see it.

So here are all the possible mating options involving an autosomal recessive like split wing:

The first possibility is that both parents are RR, thus neither shows a split wing and neither even carries the gene for split wing.  100% of their offspring would be RR, thus there would be no genetics for split wing in the line or possible at all.  This is ideal if you don’t want split wing in the birds.

103_0523

The next possibility would be that both parents are rr, thus both parents actively show the split wing on their body.  100% of their offspring would also actively have split wing.  This is ideal if you DO want split wing in your birds.  As I understand it certain Asian breeds are supposed to have split wing.  I do not understand why, but that is a whole different topic.

103_0528Another possibility would be if one parent was RR (no split wing genetics at all) and one was rr (actively has split wing).  Their offspring would be 100% Rr, which means they would carry the gene for split wing and pass it on to their offspring, but they wouldn’t actively show the split wing on their body.  They would all be carriers.

103_0606

Another possible mating would be one parent being RR (no split wing) and one being a Rr (a carrier of the gene).  They would have 50% offspring that are RR (no split wing), and 50% Rr (carriers).  Neither of the parents show it on their body, and none of the offspring show it either, but the genes are still being passed down.

103_0524Yet another possibility would be to mate two carriers to each other (Rr, no sign of split wing, but carrying the gene).  They would have 25% offspring RR (no split wing at all), 50% carriers (Rr), and 25% rr (actively showing split wing). 103_0527

The last possible mating would be a carrier (Rr) to a split wing (rr).  This would result in 50% carriers (Rr) and 50% split wings (rr).103_0526So now that I have explained how the genetics of split wing work, in my next post I am going to discuss how this affects our current breeding program with our current stock.

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